The Buddha agrees that though Nirvana should be the ultimate goal for all samsaric existences, the attainment of it is difficult to comprehend as it is beyond that outlined in any human experience. In Aggi-Vacchagotta Sutta he likens it to the cessation and extinguishing of a fire where the materials for sustenance has been removed:"Profound, Vaccha, is this phenomenon, hard to see, hard to realize, tranquil, refined, beyond the scope of conjecture, subtle, to-be-experienced by the wise.""'the liberated mind (citta) that no longer clings' means Nibbāna" (Majjhima Nikaya 2-Att. 4.68).

In Mahāyāna Buddhism, calling nirvāṇa the "opposite" of saṃsāra or implying that it is apart from saṃsāra is doctrinally problematic. According to early Mahāyāna Buddhism, they can be considered to be two aspects of the same perceived reality. By the time of Nāgārjuna, there are teachings of the identity of nirvāṇa and saṃsāra. However, even here it is assumed that the natural man suffers from at the very least a confusion regarding the nature of saṃsāra.

It is probably best to understand the relationship between Nirvāṇa and saṃsāra in terms of the Buddha while on earth. Buddha was both in saṃsāra while having attained to Nirvāṇa so that he was seen by all, and simultaneously free from saṃsāra.

The nature of Nirvāṇa assumes a differently aspected Mahāyāna focus in the Mahayana Mahaparinirvana Sutra or Nirvana Sutra, which alleges to be the final of all Mahāyāna sutras, delivered - the sutra indicates - by the Buddha on his last day of life on earth. Here, as well as in a number of related "tathagatagarbha" sutras, in which the Tathagatagarbha is equated with the Buddha's eternal Self or eternal nature, Nirvāṇa is spoken of by the Mahāyāna Buddha in very "cataphatic", positive terms. Nirvāṇa, or "Great Nirvāṇa", is indicated to be the sphere or domain (vishaya) of the True Self. It is seen as the state which constitutes the attainment of what is "Eternal, the Self, Bliss, and the Pure". Mahā-nirvāṇa ("Great Nirvāṇa") thus becomes equivalent to the ineffable, unshakeable, blissful, all-pervading and deathless Selfhood of the Buddha himself - a mystery which no words can adequately reach and which, according to the Nirvāṇa Sutra, can only be fully known by an Awakened Being - a perfect Buddha - directly.